Several methods have been considered for incorporating fingerprint sensing functionality into touch screen displays. In some proposals, the fingerprint sensing functionality is added by inserting several layers of circuitry above the display structures. In these designs, the additional layers over the display can degrade image quality.
Systems that capture a fingerprint by sensing electric fields may not function well when located entirely beneath a liquid crystal display (LCD) layer or a light-emitting diode (LED) layer of a display panel. The structure of the LCD layer and the LED layer can act as an electrical shield, which prevents the system from reading the fingerprint. In situations where this electric shield effect can be avoided, the distance through the LCD and LED layer may be too great for the system to accurately read the fingerprint.